1. Field of the Invention
The invention relates generally to the art of axle/suspension systems for heavy-duty vehicles. More particularly, the invention relates to air-ride axle/suspension systems for heavy-duty vehicles which utilize an air spring to cushion the ride of the vehicle. More specifically, the invention relates to a mechanical stop for use with an axle/suspension system that utilizes an air spring with damping characteristics that is lightweight and limits the downward movement of the beam of the axle/suspension system to minimize potential damage to the air spring and the axle/suspension system during operation of the vehicle.
2. Background Art
The use of air-ride trailing and leading arm rigid beam-type axle/suspension systems has been very popular in the heavy-duty truck and tractor-trailer industry for many years. Although such axle/suspension systems can be found in widely varying structural forms, in general their structure is similar in that each system typically includes a pair of suspension assemblies. In some heavy-duty vehicles, the suspension assemblies are connected directly to the primary frame of the vehicle. In other heavy-duty vehicles, the primary frame of the vehicle supports a subframe, and the suspension assemblies connect directly to the subframe. For those heavy-duty vehicles that support a subframe, the subframe can be non-movable or movable, the latter being commonly referred to as a slider box, slider subframe, slider undercarriage, or secondary slider frame. For the purpose of convenience and clarity, reference herein will be made to main members, with the understanding that such reference is by way of example, and that the present invention applies to heavy-duty vehicle axle/suspension systems suspended from main members of: primary frames, movable subframes and non-movable subframes.
Specifically, each suspension assembly of an axle/suspension system includes a longitudinally extending elongated beam. Each beam typically is located adjacent to and below a respective one of a pair of spaced-apart longitudinally extending main members and one or more cross members which form the frame of the vehicle. More specifically, each beam is pivotally connected at one of its ends to a hanger which in turn is attached to and depends from a respective one of the main members of the vehicle. An axle extends transversely between and typically is connected by some means to the beams of the pair of suspension assemblies at a selected location from about the mid-point of each beam to the end of the beam opposite from its pivotal connection end. The beam end opposite the pivotal connection end also is connected to an air spring, or its equivalent, which in turn is connected to a respective one of the main members. A height control valve is mounted on the main member or other support structure and is operatively connected to the beam and to the air spring in order to maintain the ride height of the vehicle. A brake system and one or more shock absorbers for providing damping to the axle/suspension system of the vehicle also are mounted on the axle/suspension system. The beam may extend rearwardly or frontwardly from the pivotal connection relative to the front of the vehicle, thus defining what are typically referred to as trailing arm or leading arm axle/suspension systems, respectively. However, for purposes of the description contained herein, it is understood that the term “trailing arm” will encompass beams which extend either rearwardly or frontwardly with respect to the front end of the vehicle.
The axle/suspension systems of the heavy-duty vehicle act to cushion the ride, dampen vibrations and stabilize the vehicle. More particularly, as the vehicle is traveling over the road, its wheels encounter road conditions that impart various forces, loads, and/or stresses, collectively referred to herein as forces, to the respective axle on which the wheels are mounted, and in turn, to the suspension assemblies that are connected to and support the axle. In order to minimize the detrimental effect of these forces on the vehicle as it is operating, the axle/suspension system is designed to react and/or absorb at least some of them.
These forces include vertical forces caused by vertical movement of the wheels as they encounter certain road conditions, fore-aft forces caused by acceleration and deceleration of the vehicle, and side-load and torsional forces associated with transverse vehicle movement, such as turning of the vehicle and lane-change maneuvers. In order to address such disparate forces, axle/suspension systems have differing structural requirements. More particularly, it is desirable for an axle/suspension system to be fairly stiff in order to minimize the amount of sway experienced by the vehicle and thus provide what is known in the art as roll stability. However, it is also desirable for an axle/suspension system to be relatively flexible to assist in cushioning the vehicle from vertical impacts, and to provide compliance so that the components of the axle/suspension system resist failure, thereby increasing durability of the axle/suspension system. It is also desirable to dampen the vibrations or oscillations that result from such forces. A key component of the axle/suspension system that cushions the ride of the vehicle from vertical impacts is the air spring, while a shock absorber typically provides damping characteristics to the axle/suspension system.
The amount of cargo that a vehicle may carry is governed by local, state, and/or national road and bridge laws. The basic principle behind most road and bridge laws is to limit the maximum load that a vehicle may carry, as well as to limit the maximum load that can be supported by individual axles. Because shock absorbers are relatively heavy, these components add undesirable weight to the axle/suspension system and therefore reduce the amount of cargo that can be carried by the heavy-duty vehicle. Depending on the shock absorbers employed, they also add varying degrees of complexity to the axle/suspension system which is also undesirable.
A pair of prior art shock absorbers of the type utilized in heavy-duty air-ride axle/suspension systems each generally include a cylinder and a piston rod reciprocating within the cylinder, although a single shock absorber has been utilized and is well known in the art. The cylinder is filled with an operating fluid, such as gas or oil, such that the operating fluid is moved by a piston valve secured to one end of the piston rod to generate a damping force.
Each one of the prior art shock absorbers is mounted on and extends between the beam of a respective one of the suspension assemblies of the axle/suspension system and a respective one of the main members of the vehicle or other component fixed to the main member, such as the hanger. Prior art shock absorbers add complexity and weight to the axle/suspension system. Moreover, because prior art shock absorbers are a service item of the axle/suspension system that require maintenance and/or replacement from time to time, they also add additional maintenance and/or replacement costs to the axle/suspension system.
Prior art shock absorbers, while providing damping characteristics, also limit the downward movement of the beam of the axle/suspension system minimizing the possibility of damage to the air spring and to the axle/suspension system. For example, when a trailer is lifted onto a railroad car, the prior art shock absorber limits downward movement of the beam of the axle/suspension system, which if not limited could potentially result in damage to the air spring and axle/suspension system. In an alternate application, the prior art shock absorber prevents the beam of the axle/suspension system from overextending downwardly when the trailer is being reversed. In this scenario, the trailer brakes are actuated and cause the axle/suspension system to extend downwardly, called “reverse braking” in the art. In another application, the axle/suspension system suddenly drops, or moves downwardly, as a result of a pothole, or other obstacle. The prior art shock absorber serves as a stop to limit the downward movement of the beam of the axle/suspension system. The limited movement of the beam of the axle/suspension system minimizes the possibility of potential damage to the air spring and axle/suspension system.
In super heavy-duty vehicles, a pair of chains are utilized to augment prior art shock absorbers to minimize the possible damage to the prior art shock absorbers as a result of such events that cause downward movement of the beam of the axle/suspension system. The prior art shock absorber and chain limit the downward movement of the beam of the axle/suspension system and thus minimize the possibility of potential damage to the air spring and the axle/suspension system.
Some axle/suspension systems, such as the one described in U.S. Pat. No. 8,540,222 owned by the same assignee of the present invention, Hendrickson USA, L.L.C., include an air spring with damping characteristics. As described in the assignee's patent, the damping shock absorber can be eliminated thus reducing complexity, saving weight and cost, and allowing the heavy-duty vehicle to haul more cargo.
The elimination of the prior art shock absorber may potentially lead to issues with downward movement of the axle/suspension system, as described previously. More specifically, the air spring and/or the axle/suspension system may be potentially damaged if the beam of the axle/suspension system overextends downwardly as a result of the trailer being lifted onto a railroad car, “reverse braking”, and/or if the trailer encounters a pot hole or other obstacle.
As set forth above, in those applications where the shock absorber has been eliminated, a need exists in the art for a mechanical stop to limit downward movement of the axle/suspension system to minimize potential damage to the air spring and/or the axle/suspension system.
The mechanical stop for axle/suspension systems of the present invention solves the problems associated with prior art axle/suspension systems that have eliminated the need for a shock absorber, by providing an apparatus for limiting the downward movement of the axle/suspension system. The mechanical stop for axle/suspension systems of the present invention includes a chain, with a plurality of links, and at least one elastomeric bushing at each end of the chain, to generally limit the downward movement of the beam of the axle/suspension system to minimize potential damage to the air spring and the axle/suspension system during operation of the vehicle.